Synthetic lubricating oils containing paraffinic resins



United States PatentO SYNTHETIC LUBRICATING OILS CONTAINING PARAFFINIC RESINS Arnold J. Morway, Clark Township, Union County, David W. Young, Westfield, and Delmer L. Cottle, Highland Park, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application February 27, 1952, Serial No. 273,776

5 Claims. (Cl. 252-42).

grease consistency with the lithium soap of a high molecular weight substantially saturated fatty acid.

In the lubrication of jet engine bearings which operate at very high temperatures the prior art greases have hitherto been lacking in some instances. In attempts to prepare greases, having the requisite high melting points and having a soap-dispersing fluid with requisitehigh flash point, grease formulations have been made from synthetic lubricating oils of the diester type exemplified by di-Z-ethyl hexyl sebacate have been prepared. However, they have generally proven unsatisfactory for this high temperature use due to low dropping points and too high volatility. Attempts to prepare greases by thickening the complex ester type synthetic oils, such as a synthetic oil prepared by reacting two molar proportions of a half ester of a dibasic acid with one molar proportion of a glycol, have been generally unsuccessful.

It has now been found and forms the object of this invention that a lubricating grease composition having desirably high temperature characteristics may be prepared by blending with a synthetic oil of the diester or complex ester type a high molecular weight resin and thickening the blend with a lithium soap of a high molecular weight fatty acid.

THE SYNTHETIC OIL The synthetic esters operable in the preferred embodiment of this invention are those esters, distillable or not distillable, which are formed by the interaction of two or more of the following compounds:

. Monohydric alcohols. Monobasic acids.

. Dibasic acids.

. Glycols.

. Polyhydric alcohols. Polybasic acids.

R-O-OC-(CH2)mC--O- OR1 where R and R1 are alkyl groups alike or different and contain from 1 to 20 carbon atoms in a straight or branched chain and where x is an integer from 2 to 10,

preferably 4 to 8. These esters include those prepared from the following acids:

Succinic acid.

Glutaric acid.

Adipic acid.

Pimelic acid.

Suberic acid.

Azelaic acid.

Sebacic acid.

Brassylic acid. Pentadecanedicarboxylic acid. Tetracosanedicarboxylic acid.

The C4-C24 alkenylsuccinic acids listed above are prepared by condensing olefins or mixtures of olefins with maleic anhydride.

The complex esters contemplated by this invention are grouped under the following types as follows:

Type I.Monobasic acid-glycol-dibasic acid-glycolmonobasic acid. This complex ester may be considered to have the following structural formula:

wherein R1 and R5 are the alkyl radicals of the monobasic acids; R2 and R4 are the alkyl radicals from the glycols; and R3 is the alkyl radical from the dibasic acid.

The esters of this type are prepared by admixing the calculated amounts of the various compounds and carrying out a straightforward esterification reaction. The re action conditions are continued with an occasional sample of the product being tested for acidity until the minimum acidity is attained.

Type II.Alcohol-dibasic acid-glycol-dibasic acid-alcohol. This material may be represented by the following formula:

wherein R1 and Rs are the combining radicals of the alcohol; R2 and R4 are the alkyl radicals of the dibasic acids; and R3 is the alkyl radical of the glycol.

These esters are prepared in the manner similar to those of Type I.

Type III.-Alcohol-dibasic acid-glycol-monobasic acid. These esters are prepared by reacting a dibasic acid and a glycol under such conditions that one hydroxyl group of the glycol combines with one carboxyl group of the dibasic acid, in other words, so that a half ester is formed. This half ester is then reacted with a molar proportion each of an aliphatic alcohol and a monobasic acid. These materials may be said to have the general formula:

wherein R1 is the combining radical of the aliphatic alcohol; R2 the alkyl radical of the dibasic acid; R3 the alkyl radical of the glycol; and R4 the alkyl radicals of the monobasic acid.

Type IV.Alcohol-dibasic acid-glycol-dibasic acidalcohol. These materials may be said to have the type formula:

wherein R1 and R5 are the combining alkyl radicals of the alcohol; R2 and R the alkyl radicals of the dibasic acid; and R3 is the alkyl radical of the glycol.

It will be noted that the esters of Type IV have the same structural formula as Type II. However, these complex esters are prepared by reacting an alcohol with a dibasic acid under such conditions that a half ester isformed and reacting two moles of such an ester with one mole of a glycol.

Type V.--Monobasic acid-glycol-dibasic acid-glycolmonobasic acid. These synthetic esters may be said to have the general formula: Ri--CO-O-R2O-O-C-R3 wherein R1 and R are the alkyl radicals of the monobasic acid; R and R4 are the alkyl radicals of the glycol; andv 2-ethylhexyl alcohol.

Cetyl alcohol.

Oleyl alcohol.

Ethylene glycol mono-n-butyl ether. Ethylene glycol-mono-Z-ethylbutyl ether. Ethylene glycol mono-2-ethylhexyl ether. Ethylene glycol mono-tert.-octyl ether. ,6-n-Butylmercaptoethanol. fi-terL-Octylmercaptoethanol. fi-n Dodecylmercaptoethanol.

Diethylene glycol mono-n-butyl ether. Diethylene glycol mono-Z-ethylbutyl ether. Propylene glycol mono-butyl thioether. Propylene glycol mono-tert.-octyl thioether. Propylene glycol mono-n-dodecyl thioether. n-Butylmercaptoethoxyethanol. tert.-Octylmercaptoethoxyethanol. n-Dodecylmercaptoethoxyethanol. n-Butylmercaptopropoxypropanol. tert.-Octylmercaptopropoxypropanol. n-Dodecylmercaptopropoxypropanol. Propylene glycol mono-n-butyl ether. Dipropylene glycol monomethyl ether. Dipropylene glycol monoethyl ether. Dipropylene glycol mono-n-butyl ether. Tripropylene glycol monomethyl ether. Tripropylene glycol monoethyl ether. Tripropylene glycol mono-n-butyl ether. Propylene glycol monoisopropyl ether. Dipropylene glycol monoisopropyl ether. Tripropylene glycol monoisopropyl ether.

Many of the above listed ether alcohols, formed by the reaction of ethylene oxide or propylene oxide with ali- ,and hydrogen upon the olefins obtainable from petroleum products. Materials such as diisobutylene and Cr olefins are suitable for this purpose; also higher and lower molecular weight olefinic materials are sometimes employed. The alcohols obtained in this manner normally have a branched chain structure.

Among the monobasic acids which may beemployed in the preparation of the esters of the present invention, the following'may be listedas illustrative:

Acetic acid. Propionic acid.

Butyric acid.

Valeric'acid.

Caproic acid.

Caprylic acid.

Laurie acid.

Palmitic acid.

Stearic acid.

Oleic acid.

{i-Methoxypropionic acid. fi-Ethoxypropionic acid. p-tert-Octoxypropionic acid. fi-Ethylmercaptopropionic acid. ,fi-tert.-Octylmercaptopropionic acid. ,B-tert.-Dodecylmercaptopropionic acid. Any of the various oxo acids.

The glycols employed in preparing the esters of the present invention include ethylene glycol and any of the paraffinic homologues of the same containing up to 18 carbon atoms. These may include, for example, ethylene glycol, propylene glycol, butylene glycols, pinacone, trimethylene glycol, tetramethylene glycol, .pentamethylene glycol, and the like. Since the glycols may also contain oxygen or sulfur atoms, compounds such as diethylene glycol, triethylene glycol, the polyethylene glycols of the formula:

HO (CHzCHzO nCHZCHZOH wherein n is 1 to 26, and the polypropylene glycols of the general formula:

R1 R2 R1 R2 HOdlH-(iJHOhtJH-(EHOH where either R1 or R2 is a methyl group and theother is hydrogen, and where n is 1 to 20, may likewisebe employed. Glycols containing sulfur atoms in thioether linkagesmay also be employed, and these include such compounds as thiodiglycol and l,2-bis(2-hydroxyethylmercapto) ethane. There also may be used glycols containing both oxygen and sulfur in similar linkages; such a compound is bis-2-(2-hydroxyethoxy) ethyl sulfide.

THE RESIN It is Well known in the art that parafiinic crude residuums especially the Pennsylvania crude residues, may be dissolved in an excess of liquid propane or other very light hydrocarbons under pressure at ordinary temperatures. The procedure generally is to use at first about two volumes of liquid propane for each volume of residuum, thesolution thereafter being cooled by allowing some of the propane to evaporate. Such cooling may cause a separation of some of the wax which may be removed. Upon addition of further propane, up to about 10 volumes per volume of residuum, and mild heating under pressure, a viscous resinous product of relatively low volatility and of high molecular Weight is precipitated in the form of a heavy oil to a plastic solid material. This resinous material has a viscosity in excess of about 300 SUS at 210 F. and a flash point in excess of 500 F. The material, per se, is well known in theprior art. It is substantially neutral, being essentially free from acids, though its exact composition is unknown. These propane precipitated resinous materials are blended with the synthetic oils mentioned above to form the base oil for the grease compositions, of the instant invention.

Blending the resinous material with the synthetic oil accomplishes several objects.

1. -It improves the high temperature properties of the grease to a point at which the composition has utility for jet engine bearing lubrication;

2. It lowers the volatility of the dispering medium. A low volatility of the dispering fluid in these high temperature greases is mandatory. Flashing oft" the liquid portion of the grease would result in heavy soap concentrations which would char or polymerize, resulting in frozen bearings.

3. It raises the viscosity of the synthetic oils which are somewhat low in viscosity in the extreme temperature range.

4. It replaces the expensive synthetic oil with a material having a decided lower cost, resulting in an obvious economic advantage.

Other advantages will become apparent as the description proceeds.

Standard inspection data on the individual components and a blend in accordance with this invention are set out in the table below:

.lVlade from: 1 mol of polyethylene glycol; 2 mols of sebacic acid; 2

moles of 2-ethyI-hexyl alcohol.

THE THICKENING SOAP H The blend of the synthetic oil and the resin is advantageously thickened with the lithium soap of a high molecular weight substantially saturated fatty acid. It is contemplated to use other alkali or alkaline metal soaps such as sodium, potassium, calcium, barium, strontium soaps of soap forming acids, however, the lithium soap is used in the preferredembodiment. Listed among those commonly used soapforming materials which are known to the art and which are operable to form the thickeningagents, of this invention are the hydrogenated fish oil acids, oleic acid, stearic acid, hydroxy stearic acids, beef fat, tallow, the saturated or unsaturated glycerides of various fatty acids, or mixtures of the above in any proportionsalthough the fatty acids rather than the glycerides are preferred.

PROPORTIONS OF COMPONENTS To form the lubricating oil' base for. the improved high temperature greases of this invention it is contemplated that a blend containing from about 20% to 50% by volume of the resinto about 80% to 50% of the synthetic oil chosen be used. Various factors will affect the component proportions used, of course, such as the type of synthetic oil used, the viscosity of the resin, the temperature at which the grease composition is to be used and the like. his generally preferred, however, to blend with a synthetic lubricating oil of the ester type about 25% to 35% by volume of a resin having a viscosity in excess of about 300 SUS at 210 F.

The amount of soap that is used to thicken the blend into a finished grease formulation will also vary according to the desired product. Generally, it has been found advantageous to thicken the blends with from to 25% by weight of the soap, with from to of the soap being preferred.

The procedure used in formulating the grease compositions of this invention is straightforward and presents no problems to those familiar with the art. Generally it is as follows: i The resin and the preformed soap are stirred together in a fire heated grease kettle and heated to a temperature of about 150-300 F. The synthetic oil is then added and the mixture stirred and heated to a temperature of about 400-430 F. is reached. The grease is then drawn into shallow pans and allowed to cool. After cooling it is homogenized by working. If desirable, inhibitors or other improving additions may be added to the grease after heat has been removed and before drawing.

If it is desired toform the soap in situ this may be done by adding the fatty acid to the kettle followed by the lithium, usually in the form of the hydroxide while only the resin is present. After complete neutralization and dehydration of the soap the complex ester is then added. By this method any hydrolysis of the ester is materially prevented.

To further describe the advantages of the grease compositions of instant invention the following examples are given:

Example I .Di-2 ethylhexyl sebacate grease About 50 parts by weight of a synthetic oil formed by esterifying sebacic acid with 2-ethyl hexanol was admixed with 20 parts by weight of lithium stearate in a fire heated grease kettle. The mixture was stirred while heating to about F. At this temperature 29 parts of the synthetic oil was added and the temperature was raised to about 410 F. At that temperature heating was stopped and about 1 part by weight of an oxidation inhibitor was added. The formulation was then drawn into pans, cooled and homogenized by working. A clear homogeneous grease product resulted which had the following properties.

ASTM penetration (mm/10):

above attempts were made to prepare a lithium soap grease using as a base oil a blend of 65% of di-octyl sebacate with 35% of a complex ester prepared by reacting together two mols of a mono 2-ethyl hexanol ester of sebacic acid with one mol of a polyethylene glycol. This blend has a flash point of 420 F., and a viscosity at 210 F. of 42.5 SUS. The attempts were unsuccessful since a mushy, grainy product resulted indicating that the soap would not disperse in the ester.

Example Ills-Grease compositions of invention A. 7.5% lithium hydroxy stearate.

7.5% lithium stearate. 1.0 oxidation inhibitor. 24.0% resin (vis. 210 F./444 SUS). 60.0% complex ester (same as in Example II).

The lithium soaps were mixed in the resin and dispersed at 350 F., when the complex ester was added and the mass heated while stirring to 420 F; the inhibitor was added and the grease cooled in shallow trays.

ASTM inspections:

Penetration (mm./10)- Unworked 265 Worked (60 strokes) 267 Worked (100,000 strokes) 295 Dropping point F.) 395 Aeration (same condition as Example I) 5% Percent evaporation at 350 F.-24 hours 1.0

B. 7.5 hydroxy stearic acid.

7.5 hydrogenated fish oil acids. 2.4% LiOH-HzO. 1.0% oxidation inhibitor. 22.6% resin (vis. 210 F./444 SUS). 59.6% complex ester (same as in Example II).

while raising the temperature to 420 F. The grease was drawn into pans for cooling and when cold returned to the kettle and homogenized by stirring .cold. Further homogenization may be accomplished by passage of the grease through a homogenizer.

ASTM inspect-ions:

Penetration (mm/10)- Unworked 255 Worked (60 strokes) 270 Worked (100,000 strokes) 300 Dropping point F.) 395 Aeration (same conditionas Ex. 1)., less than 5% Percent evaporation at 350 F.-24 hours 1.0

ASTM inspections:

Penetration (mm./)--

Unworked 265 Worked (60 strokes) 265 Worked (100,000 strokes) 285 Dropping point F.) 380 Aeration (beater test) None Percent evaporation at 350 F.'24 hours less than 1.0

It is to be seen that the grease compositions of this invention have outstanding high temperature properties as shown by their structure stability and their high dropping points.

To summarize briefly, this invention relates to high temperature lubricating grease compositions useful for the lubrication of jet engine bearings. The grease compositions are prepared by thickening to a grease consistency a lubricating oil-blend'with a lithium soap of a high molecular weight substantially saturated fatty acid. The lubricating oil blend comprises a synthetic oil from to 50% by volume of a resinous material extracted from a parafiinic crude residue by propane precipitation. The resinuous materials operable have viscosities ranging from about 300 to 1500 SUS at 210 F.,and have flash points in excess of about 500 F. The synthetic oils are preferably of the ester type, either a simple ester as exemplified by di-2-ethylhexyl sebacate, a complex ester, such as the reaction product of two moles of a dibasic acid half-ester with one mole of a polyglycol, or mixtures of these types.

What is claimed is:

1. A lubricating grease composition having outstanding high temperature properties which comprises 50 to 80% by volume of at least one synthetic lubricating oil selected from the group consisting of (a) a diester lubricating oil having the formula wherein R and R1 are alkyl groups having from 1 to 20 carbon atoms and x is an integer from 2 to 10, and (b) acornplex ester having the formula wherein R1 and R5 are monohydric alcohol alkyl radicals, R2 and R4 are dibasic acid alkyl radicals, and R3 is a glycol alkyl radical, containing combined therein about 20 to 50% by volume of a propane precipitated parafiinic resinhaving a viscosity in excess of 300 SUS at 210 F. thickened to a grease consistency with a lithium soap of a high molecular weight saturated fatty acid.

2. The lubricating grease composition of claim 1 wherein said synthetic lubricating oil is said complex ester lubricating oil containing combined therein about 25 to 35% by volume of said propane precipitated parafiinic resin.

3. The lubricating grease composition of claim 2 wherein said lithium soap is present in an amount from 10 to 25% by weight.

4. A lubricating grease composition having outstanding high temperature properties which consists essentially of about 50 to 80% by volume of di-2ethyl-hexyl sebacate containing combined therein about 20% to 50% by volume of a propane precipitated parafiinic resin having a viscosity in excess of 300 SUS at 210 F. thickened to a grease consistency with from 15% to 20% by weight of a lithium soap of a high molecular weight saturated fatty acid.

5. A lubricating grease composition having outstanding high temperature properties which consists essentially of 50 to 80% by volume of a synthetic lubricating oil consisting essentially of di-octyl sebacate and 35% of the reaction product of 2 moles of sebacic acid, 2 moles of Z-ethyl-hexyl alcohol and 1 mole of a polyethylene glycol containing combined therein about 20% to 50% by volume of a propane precipitated paraflinic resin having a viscosity in excess of 300 SUS at 210 F. thickened to'a grease consistency with from 15% to 20% by weight of a lithium soap of a high molecular Weight saturated fatty acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,378,818 Zimmer et al.. June 19, 1945 2,436,347 Zimmer et al. Feb. 17, 1948 2,450,222 Ashburn et al Sept. 28, 1948 2,477,311 Morway July 26, 1949 2,491,028 Beerbower Dec. 13, 1949 2,521,438 Zimmer et al Sept. 5, 1950 2,570,037 Smith et al Oct. 2, 1951 2,575,195 Smith Nov. 13, 1951 2,575,196 Smith Nov. 13,1951 2,591,054 Morway Dec. 13, 1949 2,629,666 Morway et al. Feb. 24, 1953' 

1. A LUBRICATING GREASE COMPOSITION HAVING OUTSTANDING HIGH TEMPERATURE PROPERTIES WHICH COMPRISES 50 TO 80% BY VOLUME OF AT LEAST ONE SYNTHETIC LUBRICATING OIL SELECTED FROM THE GROUP CONSISTING OF (A) A DIESTER LUBRICATING OIL HAVING THE FORMULA 